Electronic vapor provision system

ABSTRACT

A control unit for an electronic vapor provision system includes a battery for providing electrical power to a heater which is used to produce vapor. The battery is a lithium iron phosphate battery. The battery provides an output voltage which remains at an approximately constant voltage level as the battery is discharged.

PRIORITY CLAIM

The present application is a continuation application of U.S. patentapplication Ser. No. 16/949,216, filed Oct. 20, 2020, which is acontinuation application of U.S. patent application Ser. No. 15/754,349,filed Feb. 22, 2018, which is a National Phase entry of PCT ApplicationNo. PCT/GB2016/052624, filed Aug. 24, 2016, which claims priority fromGB Patent Application No. 1515087.3, filed Aug. 25, 2015, each of whichis hereby fully incorporated herein by reference.

FIELD

The present disclosure relates to an electronic vapor provision system,e.g. an e-cigarette, and to a control unit for such a system.

BACKGROUND

Electronic vapor provision systems such as e-cigarettes and otherelectronic nicotine delivery systems generally contain a cartridge toprovide a reservoir of liquid which is to be vaporized, typicallynicotine. When a user inhales on the device, a control unit operates abattery to provide power to a heater. This activates the heater tovaporize a small amount of liquid, which is then inhaled by the user.

This type of e-cigarette therefore generally incorporates twoconsumables, firstly the liquid to be vaporized, and secondly power inthe battery. Regarding the former, once the reservoir of liquid has beenexhausted, at least a portion of the device containing the cartridge maybe discarded to allow replacement with a new cartridge. Regarding thelatter, an e-cigarette usually provides some form of electricalconnector to receive power from an external charging device, therebyallowing the battery with the e-cigarette to be re-charged.

Most e-cigarettes are powered by re-chargeable lithium ion batteries (orcells), which are to be found in a very widespread range of devices, notjust e-cigarettes. (N.B. the terms “battery” and “cell” will be usedinter-changeably herein, since due to the limited space within ane-cigarette, the battery in such an e-cigarette usually comprises just asingle cell.) Conventional (commonly-used) lithium ion batteries arebased on a cathode made from lithium cobalt oxide (LiCoO₂), and producea voltage output that tends to decline as they discharge, for example,from about 4.2V when fully charged, down to about 3.0V before beingfully depleted, i.e. a decline of about 28%. Furthermore, since thepower output across a given heating resistor R goes with V²/R, thisimplies that there would generally be a corresponding drop in poweroutput such that the final operational power output (at a voltage of3.0V) is only 52% of the initial power output (at a voltage of 4.2V).This change in power supplied by the battery to the heater, from beingfully charged to being nearly discharged, can therefore significantlyimpact the amount of liquid vaporized, and hence inhaled by a user.

Existing e-cigarettes have adopted a number of techniques for copingwith this variation in power supplied by a battery over the dischargecycle. For example, some devices may shut themselves down before thebattery falls to 3.0V—e.g. at a battery output voltage of 3.6V. Thisreduces the variation in power output (the final operational poweroutput is now at about 73% of the maximum value for a 3.6V cut-off). Onthe other hand, part of the energy stored within the battery is nolonger available for use, which reduces the time that the device can beoperated without having to then re-charge.

Other devices employ a capacitor to store additional charge from thebattery. By suitable switching the capacitor can then be used as anadditional (temporary) power source to supplement the voltage availablefrom the battery. This supplementary power (voltage) from the capacitorcan thereby help to compensate for the reduced voltage available fromthe battery in the latter stages of the discharge cycle.

Another approach is to use a pulse width modulation (PWM) scheme, inwhich the power is supplied from the battery as a succession ofrectangular pulses. If the duration (width) of each pulse is P, and thepulse interval from the end of one pulse to the start of the next pulseis I, then we can define the PWM duty cycle (D) as D=P/(P+I). The dutycycle goes to zero as the pulse width P goes to zero, i.e. in this casethe battery is effectively not supplying power. Conversely, the dutycycle goes to unity as the pulse interval I goes to zero, i.e. in thiscase the battery is effectively supplying continuous (unmodulated)power. If the voltage output from the battery is V, where 3.6<V<4.2,then we can set the duty cycle D such that the effective voltage output,DV, has a constant value, for example, 3.6V. In particular, if thecurrent voltage output from the battery is V=3.6, i.e. the battery isnearly depleted, the PWM is set such that D=1, while if the currentvoltage output from the battery is V=4.2, i.e. the battery is fullycharged, the PWM is set such that D=0.857 (with intermediate values of Das appropriate for intermediate values of the battery output voltage).

Note that a PWM scheme to control the output of voltage from the batterymay be used for more general control purposes (rather than specificallyto compensate for variation in battery voltage output). For example, theheater power output may be measured, such as by using some form ofthermometer, or by electrically monitoring the current and/or voltagesupplied to the heater. The PWM duty cycle may then be controlled toobtain a desired output temperature from the heater. It will beappreciated that such a control system may accommodate variations inbattery voltage output along with other potential variations (such asexternal temperature, type of liquid to be vaporized, etc.).Furthermore, such a control system may use some other mechanism (notPWM) to regulate the effective output voltage and power from thebattery.

Existing schemes to accommodate variations in battery output voltagehave certain drawbacks. For example, they usually require additionalcomponents in the e-cigarette, which adds to complexity and cost.Moreover, a PWM system (or similar) may constrain power based on thelowest battery output voltage (v=3.6). In other words, at higher levelsof available battery output voltage (such as V=4.2), the availableoutput voltage is reduced (by PWM or any other suitable mechanism),which effectively chokes back the performance. Such an approachtherefore prevents a user from experiencing the operation of the deviceat full battery voltage.

SUMMARY

The disclosure is defined in the appended claims.

A control unit for an electronic vapor provision system includes abattery for providing electrical power to a heater which is used toproduce vapor. The battery is a lithium iron phosphate battery. Thebattery provides an output voltage which remains at an approximatelyconstant voltage level as the battery is discharged.

An electronic vapor provision system is also provided which includessuch a control unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the disclosure will now be described in detail byway of example only with reference to the following drawings:

FIG. 1 is a schematic (exploded) diagram of an e-cigarette in accordancewith some embodiments of the disclosure.

FIG. 2 is a schematic diagram of the body of the e-cigarette of FIG. 1in accordance with some embodiments of the disclosure.

FIG. 3 is a schematic diagram of the cartomizer of the e-cigarette ofFIG. 1 in accordance with some embodiments of the disclosure.

FIG. 4 is a schematic diagram of certain electrical components of thee-cigarette of FIG. 1 in accordance with some embodiments of thedisclosure.

FIGS. 5 and 6 are schematic graphs that compare certain operationalproperties of an LFP battery (solid line) with those of a commonly usedlithium ion battery (dashed line) in the context of e-cigarettes.

FIGS. 7, 8 and 9 are graphs of experimental data showing voltage (topline) and current (lower line) against used capacity during simulateduse of an e-cigarette. For FIG. 7 , the simulated use involves drawingrepeated current pulses of 4 A from the battery, for FIGS. 8 and 9 thesimulated use involves drawing repeated current pulses of 5 A from thebattery. For FIGS. 7 and 8 , the battery is a lithium iron phosphate(LFP) battery in accordance with some embodiments of the disclosure; forFIG. 9 , the battery is a lithium manganese battery. In all cases, thebattery has an AA form factor.

FIG. 10 is a tabular representation of the experimental data shown inFIG. 7 .

DETAILED DESCRIPTION

As described above, the present disclosure relates to a battery-poweredelectronic vapor provision system, such as an e-cigarette. Throughoutthe following description the term “e-cigarette” is used; however, thisterm may be used interchangeably with electronic vapor provision system.Such an electronic vapor provision system may be based, for example, onthe vaporization (by heating) of a liquid, where the liquid includesnicotine, and a user then inhales the resulting vapor containingnicotine. Another possibility is that the electronic vapor provisionsystem includes material derived from tobacco plants. This tobaccomaterial may be provided in any suitable form (powder, paste, shreddedleaf material, etc.). The tobacco material may be heated to producevolatiles for inhalation by a user. The skilled person will be aware ofvarious other forms of electronic vapor provision system which canutilize battery power as described herein for heating a substance toproduce vapor.

FIG. 1 is a schematic (exploded) diagram of an e-cigarette 10 inaccordance with some embodiments of the disclosure (not to scale). Thee-cigarette has a generally cylindrical shape, extending along alongitudinal axis indicated by dashed line LA, and comprises two maincomponents, namely a body 20 and a cartomizer 30. The cartomizer 30includes an internal chamber containing a reservoir of liquid, avaporizer (such as a heater), and a mouthpiece 35. The liquid in thereservoir typically includes nicotine in an appropriate solvent, and mayinclude further constituents, for example, to aid aerosol formation,and/or for additional flavoring. The reservoir may include a foam matrixor any other structure for retaining the liquid until such time that itis required to be delivered to the vaporizer. The cartomizer 30 mayfurther include a wick or similar facility to transport a small amountof liquid from the reservoir to a heating location on or adjacent theheater. The control unit 20 includes a re-chargeable cell or battery toprovide power to the e-cigarette 10 and a circuit board for generallycontrolling the e-cigarette 10. When the heater receives power from thebattery, as controlled by the circuit board, the heater vaporizes theliquid from the wick and this vapor is then inhaled by a user throughthe mouthpiece 35.

The control unit 20 and cartomizer 30 are detachable from one another byseparating in a direction parallel to the longitudinal axis (LA) of thee-cigarette 10, as shown in FIG. 1 , but are joined together when thedevice 10 is in use by a connection, indicated schematically in FIG. 1as 25A and 25B, such as a bayonet or screw fitting. This connectionprovides mechanical and electrical connectivity between the body 20 andthe cartomizer 30. The electrical connector on the body 20 that is usedto connect to the cartomizer may also serve as a socket for connecting acharging device (not shown) when the body 20 is detached from thecartomizer 30. The other end of the charging device can be plugged intoa USB socket to re-charge the battery in the control unit 20 of thee-cigarette 10. In other implementations, a cable may be provided fordirect connection between the electrical connector on the body 20 and aUSB socket. In other implementations, the re-charging of the battery inthe control unit 20 may be performed via the tip end 225 of thee-cigarette 10, i.e. the end opposite to the mouthpiece 35.

The control unit 20 is provided with one or more holes (not shown inFIG. 1 ) for air inlet. These holes connect to an air passage throughthe control unit 20 to an air passage provided through the connector 25.This then links to an air path through the cartomizer 30 to themouthpiece 35. When a user inhales through the mouthpiece 35, air isdrawn into the control unit 20 through the one or more air inlet holes,which are suitably located on the outside of the e-cigarette 10. Thisairflow (or the resulting change in pressure) is detected by a pressuresensor that in turn activates the heater to vaporize the liquid from thereservoir (via the wick). The airflow passes from the control unit,through the vaporizer, where it combines with the vapor, and thiscombination of airflow and (nicotine) vapor then passes through thecartomizer 30 and out of the mouthpiece 35 to be inhaled by a user. Thecartomizer 30 may be detached from the body 20 and disposed of when thesupply of liquid is exhausted and replaced with another cartomizer 30,if so desired. (The cartomizer 30 may therefore sometimes be referred toas a disposable component, and the control unit 20 as a re-usablecomponent.)

It will be appreciated that the e-cigarette 10 shown in FIG. 1 ispresented by way of example, and various other implementations can beadopted. For example, in some embodiments, the cartomizer 30 is providedas two separable components, namely a cartridge comprising the nicotinereservoir and mouthpiece (which can be replaced when the liquid from thereservoir is exhausted), and a vaporizer comprising a heater (which isgenerally retained). As another example, the charging facility mayconnect to an additional or alternative power source, such as a carcigarette lighter.

FIG. 2 is a schematic (simplified) diagram of the control unit 20 of thee-cigarette 10 of FIG. 1 in accordance with some embodiments. FIG. 2 cangenerally be regarded as a cross-section in a plane through thelongitudinal axis LA of the e-cigarette 10. Note that certain componentsand details of the body 20, e.g. wiring and more complex shaping, havebeen omitted from FIG. 2 for reasons of clarity.

As shown in FIG. 2 , the control unit 20 includes a battery 210 forpowering the e-cigarette 10, as well as a printed circuit board (PCB)202 on which is mounted a chip, such as an application specificintegrated circuit (ASIC) or microcontroller, for controlling thee-cigarette 10. The PCB 202 may be positioned alongside or at one end ofthe battery 210. In the configuration shown in FIG. 2 , the PCB 202 islocated between the battery 210 and the connector 25B. The control unitalso includes a sensor unit 215 to detect an inhalation on mouthpiece35. In the configuration shown in FIG. 2 , the sensor unit 215 islocated between the battery 210 and the tip end 225, but in otherimplementations, it may be located on or adjacent to PCB 202 (which maybe positioned as shown in FIG. 2 , or in some other location). Inresponse to such a detection of inhalation, the sensor unit 215 notifiesthe chip on the PCB 202, which in turn initiates the flow of power fromthe battery 210 to a heater in the cartomizer 30.

The tip end 225 of the control unit 20 includes a cap to seal andprotect the far (distal) end of the e-cigarette 10. There is an airinlet hole provided in or adjacent to the cap to allow air to enter thebody 20 and flow past the sensor unit 215 when a user inhales on themouthpiece 35. This airflow therefore allows the sensor unit 215 todetect the user inhalation. In some implementations, the tip end 225 maybe provided with a light, such as a light emitting diode (LED) that isilluminated by the chip in response to the detection of inhalation bythe sensor unit 225. The tip end 225 may also (or alternatively) beprovided with an electrical contact (not shown in FIG. 2 ) to provide anadditional connection for re-charging battery 210.

At the opposite end of the body 20 from the tip end 225 is the connector25B for joining the control unit 20 to the cartomizer 30. As notedabove, the connector 25B provides mechanical and electrical connectivitybetween the control unit 20 and the cartomizer 30. As shown in FIG. 2 ,the connector 25B includes a body connector 240, which is metallic(silver-plated in some embodiments) to serve as one terminal forelectrical connection (positive or negative) to the cartomizer 30. Theconnector 25B further includes an electrical contact 250 to provide asecond terminal for electrical connection to the cartomizer 30 ofopposite polarity to the first terminal, namely body connector 240. Theconnector 240 generally has an annular ring shape, while contact 250 islocated in the center of this ring (when seen in a plane which isperpendicular to the longitudinal axis, LA, of the e-cigarette 10).

The electrical contact 250 is mounted on a coil spring 255. When thecontrol unit 20 is attached to the cartomizer 30, the connector 25A onthe cartomizer pushes against the electrical contact 250 in such amanner as to compress the coil spring 255 in an axial direction, i.e. ina direction parallel to (co-aligned with) the longitudinal axis LA. Inview of the resilient nature of the spring 255, this compression biasesthe spring 255 to expand, which has the effect of pushing the electricalcontact 250 firmly against connector 25A, thereby helping to ensure goodelectrical connectivity between the control unit 20 and the cartomizer30. The body connector 240 and the electrical contact 250 are separatedby a trestle 260, which is made of a non-conductor (such as plastic) toprovide good insulation between the two electrical terminals. Thetrestle 260 is shaped to assist with the mutual mechanical engagement ofconnectors 25A and 25B.

FIG. 3 is a schematic diagram of the cartomizer 30 of the e-cigarette 10of FIG. 1 in accordance with some embodiments of the disclosure. FIG. 3can generally be regarded as a cross-section in a plane which includesthe longitudinal axis LA of the e-cigarette 10. Note that variouscomponents and details of the control unit 20, e.g. wiring and morecomplex shaping, have again been omitted from FIG. 3 for reasons ofclarity.

The cartomizer 30 includes an air passage 355 extending along thecentral (longitudinal) axis of the cartomizer 30 from the mouthpiece 35to the connector 25A for joining the cartomizer to the control unit 20.A reservoir of liquid 360 (typically including nicotine in a solvent) isprovided around the air passage 335. This reservoir 360 may beimplemented, for example, by providing cotton or foam soaked in theliquid. The cartomizer 30 also includes a heater 365 for heating theliquid from reservoir 360 to generate (nicotine-containing) vapor toflow through air passage 355 and out through mouthpiece 35 in responseto a user inhaling on the e-cigarette 10. The heater 365 is poweredthrough lines 366 and 367, which are in turn connected to opposingpolarities (positive and negative, or vice versa) of the battery 210 viaconnector 25A. (As noted above, the details of the wiring between thepower lines 366 and 367 and connector 25A are omitted from FIG. 3 .)

The connector 25A includes an inner electrode 375, which may besilver-plated or made of some other suitable metal. When the cartomizer30 is connected to the control unit 20, the inner electrode 375 contactsthe electrical contact 250 of the control unit 20 to provide a firstelectrical path between the cartomizer 30 and the control unit 20. Inparticular, as the connectors 25A and 25B are engaged, the innerelectrode 375 pushes against the electrical contact 250 so as tocompress the coil spring 255, thereby helping to ensure good electricalcontact between the inner electrode 375 and the electrical contact 250.

The inner electrode 375 is surrounded by an insulating ring 372, whichmay be made of plastic, rubber, silicone, or any other suitablematerial. The insulating ring 372 is surrounded by the cartomizerconnector 370, which may be silver-plated or made of some other suitablemetal or conducting material. When the cartomizer 30 is connected to thecontrol unit 20, the cartomizer connector 370 contacts the bodyconnector 240 of the control unit 20 to provide a second electrical pathbetween the cartomizer 30 and the control unit 20. In other words, theinner electrode 375 and the cartomizer connector 370 serve as positiveand negative terminals (or vice versa) for supplying power from thebattery 210 in the control unit 20 to the heater 365 in the cartomizer30 via supply lines 366 and 367 as appropriate.

The cartomizer connector 370 is provided with two lugs or tabs 380A,380B, which extend in opposite directions away from the longitudinalaxis LA of the e-cigarette 10. These tabs 380A, 380B are used to providea bayonet fitting in conjunction with the body connector 240 forconnecting the cartomizer 30 to the control unit 20. This bayonetfitting provides a secure and robust connection between the cartomizer30 and the control unit 20, so that the cartomizer 30 and control unit20 are held in a fixed position relative to one another, without wobbleor flexing, and the likelihood of any accidental disconnection is verysmall. At the same time, the bayonet fitting provides simple and rapidconnection and disconnection by an insertion followed by a rotation forconnection, and a rotation (in the reverse direction) followed bywithdrawal for disconnection. It will be appreciated that otherembodiments may use a different form of connection between the controlunit 20 and the cartomizer 30, such as a snap fit or a screw connection.

FIG. 4 is a schematic diagram of certain electrical (includingelectronic) components of the e-cigarette 10 of FIG. 1 in accordancewith some embodiments of the disclosure. These components are generallylocated in the control unit 20, since this is a re-usable (rather thandisposable) portion. However, in some embodiments at least, some of theelectrical components may be located in the cartomizer 30.

As shown in FIG. 4 , the control unit 20 includes an electrical (andmechanical) connector 25B (as discussed above), a power switch 212, abattery 210, a processor or (micro)controller 555, a communicationsinterface 217, a speaker 558, and a sensor unit 215. The controller 555is located on PCB 202, which may also be used for mounting othercomponents as appropriate, e.g. sensor unit 215, power switch 212,and/or communications interface 217, depending upon the particularinternal configuration of the control unit 202. Alternatively, thesecomponents may be located on one or more other PCBs (or other forms ofmounting).

FIG. 4 illustrates some, but not necessarily all, of the electricalconnections between the different components. For example, the sensorunit 215 may receive power from the battery 210 via its connection tothe controller 555, or alternatively there may be a separate powerconnection from the battery 210 direct to the sensor unit 215 (notshown).

The sensor unit 215 is located in or adjacent to the air path throughthe control unit 20 from the air inlet to the air outlet (to thevaporizer). The sensor unit 215 includes a pressure sensor 562 and atemperature sensor 563 (also in or adjacent to this air path). Note thatin some embodiments, there may be additional sensors (not shown in FIG.4 ); also, the pressure sensor 562 and temperature sensor 563 may beprovided as different devices (rather than being combined into a singlesensor unit). The pressure sensor 562 may detect airflow by looking fora pressure drop caused by inhalation on the mouthpiece 35 (oralternatively the pressure sensor 562 may detect an inhalation bydirectly measuring airflow, analogous to an anemometer measuring wind).

The controller 555 includes a processor such as a CPU and memory (ROMand RAM). The operations of the controller 555 and other electroniccomponents, such as the pressure sensor 562, are generally controlled atleast in part by software programs running on the processor (or on theother electronic components as appropriate). Such software programs maybe stored in a non-volatile memory, such as ROM, which can be integratedinto the controller 555 itself, or provided as a separate component(e.g. on PCB 202). The processor may access the ROM to load and executeindividual software programs as and when required. The controller 555also contains suitable interfaces (and control software) for interactingwith the other devices, such as with the sensor unit 215.

The controller 555 utilizes the speaker 58 as an output device forproducing audio signals to indicate conditions or states within thee-cigarette 10, such as a low battery warning. Different signals forsignaling different states or conditions may be provided by utilizingtones or beeps of different pitch and/or duration, and/or by providingmultiple such beeps or tones. Other forms of output device may beprovided as well as or instead of the speaker 58. For example, asmentioned above the tip end 225 may be provided with a light emittingdiode (LED) which may be used for signaling and/or ornamentation. Theremay also (or alternatively) be a light output at one or more otherlocations on the e-cigarette 10.

The communications interface 217 may be a wired or wireless connectionto allow the e-cigarette 10 to communicate with an external device. Forexample, the communications interface 217 may support one or more ofBluetooth, Wi-Fi (the IEEE 802.11 family), and/or near fieldcommunications (NFC) for establishing wireless communications.Alternatively, or additionally, the communications link may supportwired communications, potentially via connector 25B and/or some othercommunications facility. The communications interface 217 may be used,inter alia, to allow an external device to provide and update controlsettings on the e-cigarette 10, and/or to retrieve status and usageinformation from the e-cigarette 10.

As noted above, the e-cigarette 10 provides an air path from the airinlet through the e-cigarette 10, past the pressure sensor 562 and theheater 365 (in the vaporizer), to the mouthpiece 35. Thus when a userinhales on the mouthpiece 35 of the e-cigarette 10, the controller 555detects such inhalation based on information from the pressure sensor562. In response to such a detection, the CPU supplies power from thebattery or cell 210 to the heater 365, which thereby heats and vaporizesthe liquid from the wick for inhalation by the user.

The battery 210 is linked to the heater 365 via a power switch 212 andconnector 25B (plus connector 25A on the cartomizer 30). The powerswitch 212 supports the flow (and switching on/off) of the relativelylarge current supplied from the battery 210 in order to power the heater365—this is typically of the order of 1 amp or more. The power switch212 is controlled by the controller 555. For example, the controller 555may close the power switch 212 in response to the pressure sensor 562sensing an airflow through the e-cigarette 10, thereby allowing power toflow from the battery 210 to the heater 365. Conversely, the controller555 may open the power switch 212 in response to the pressure sensor 562sensing that the airflow through the e-cigarette 10 has now ended,thereby terminating the power flow from the battery 210 to the heater365. In addition, the controller 555 may use switch 212 to implement aPWM scheme, as described above, to regulate the amount of power suppliedfrom the battery 210 to the heater 365 during an inhalation.

It will be appreciated that the electrical configuration shown in FIG. 4is provided by way of example only, and the skilled person will be awareof many potential variations. For example, some e-cigarettes 10 may nothave a communications interface 217, while in other embodiments, thecommunications interface 217 may be combined, at least in part, with thecontroller 555. Similarly, some of the functionality of the controller555 may be distributed across one or more other devices. For example,there may be a PCB provided in combination with battery 210 to controlre-charging of the battery 210, such as to detect and thereby preventvoltage or current overload and/or overly long charging, and likewise tocontrol discharging of the battery 210, e.g. so that the battery doesnot get excessively discharged to the point of damage. Such batterycontrol functions may also be integrated into the processor orcontroller 555 (or into some other device).

The battery 210 is a lithium iron phosphate (LFP) battery which useslithium ferrophosphate, LiFePO₄, for the cathode. LFP batteries havecertain advantages and disadvantages compared with other availablebatteries, such as other types of lithium ion batteries, including thecommonly used cobalt cathode battery, or variants thereof (e.g. having asolid rather than liquid electrolyte, or using a silicon anode ratherthan a graphite anode). However, it has been found that the propertiesof LFP batteries are particularly well-suited for use in an e-cigarette,based (primarily) on the following factors:

-   -   non-toxicity. This is important for a product which is used        (albeit not consumed) orally, for example, if the product has        been inadvertently damaged. The lack of toxicity also gives        improved environment properties (compared to cobalt as used in        most common lithium ion batteries), especially since        e-cigarettes are a relatively high-volume, low cost product, and        may not always be disposed of in an approved manner—e.g. if the        product is accidentally dropped or otherwise lost while outside.    -   thermal, electro-chemical, and structural stability. The thermal        stability is important for a product which is used in (and hence        exposed to) a wide range of weathers and temperature conditions.        Also the good electro-chemical and mechanical stability reduces        the risk of fire, etc., which has been a problem for most common        lithium ion batteries, as reported, for example, on 4 Feb. 2014        in “Batteries on planes pose ‘increased fire risk’”        (http://www.bbc.co.uk/news/business-25733346).    -   constant discharge voltage. As noted above, most common lithium        ion batteries tend to have an output voltage that decreases        steadily over the discharge cycle from about 4.2V down to about        3.6V. This can lead to an inconsistent user experience in terms        of supplied vapor (dependent on the current voltage level), or        else require an e-cigarette to incorporate appropriate        electronics to compensate for this decrease in output voltage,        which leads to additional expense and complexity (in what is a        relatively high-volume, low cost product).    -   high peak current/power. LFP batteries can support a higher peak        current (and hence higher peak power) than most common lithium        ion batteries. This is attractive for e-cigarettes, because it        allows the heater to power up more quickly to the correct        operating temperature for vaporization in response to the        detection of a user inhalation, and hence makes the e-cigarette        more user-responsive.    -   a slower rate of capacity loss (self-discharge) when the battery        is not in use. This gives improved shelf (calendar) life if a        product is to be supplied ready-charged (which is the case for        many e-cigarettes in order to allow for rapid use after purchase        by a consumer).    -   a large number of re-charge cycles are possible—e.g. up to or        over 2000. This gives several years of use even if re-charging        occurs on a daily basis (see below).

LFP batteries do have a lower energy density than most common lithiumion batteries. However, whereas most common lithium ion batteries areutilized in electronic devices that may be subject to continuous andintensive use (such as smartphones), so that battery lifetime isespecially significant in such devices, e-cigarettes tend to have adifferent usage profile. In particular, there is an interval betweensuccessive activations (puffs) of an e-cigarette, and indeed somee-cigarettes may provide protection against over-use, e.g. by monitoringand regulating for a maximum number of puffs in a given time period(after which the processor may prevent further activation until the timeperiod has expired). Accordingly, the lower energy density of LFPbatteries (compared with most common lithium ion batteries) is moreacceptable for e-cigarettes than for most other electronic devices.

Nevertheless, LFP batteries do have sufficient energy density to supportreasonable use of an e-cigarette. For example, an AA-sized LFP batterymay have a rated capacity of 250-600 mA hours, whereas a correspondingcommonly-used lithium ion battery may have a rated capacity of 600-750mA hours or more (and operate at a higher voltage), depending on factorssuch as discharge current. Of course, some e-cigarettes may be too smallfor an AA-sized battery, and accordingly their battery capacity wouldhave to be reduced accordingly. Nevertheless, given that a typical puffof a regular e-cigarette uses of the order of 1-4 mA hours (depending onthe particular nature of the device and the amount of liquid to bevaporized), a reasonably-sized LFP battery is capable of providing atleast 100 puffs (and potentially many more) before discharging.Therefore, if we assume that the e-cigarette is re-charged on a dailybasis, this number of puffs per battery charge cycle is sufficient formost consumers.

FIGS. 5 and 6 are graphs that compare certain operational properties ofan LFP battery (solid line) with those of a commonly-used lithium ionbattery (dashed line) in the context of e-cigarettes. (Please note thatthese graphs are highly schematic and simplified for ease ofunderstanding; some more accurate graphs are presented below.) FIG. 5illustrates in schematic form how the voltage output of the battery 210varies with time, typically over a timescale of many hours or daysduring the discharge cycle (from fully charged to discharged). Asdiscussed above, as a commonly-used lithium ion battery discharges, theoutput voltage steadily declines from about 4.2V down to about 3.6V (orbelow). This decline in output voltage may result in a noticeable change(drop) in performance, such as the amount of nicotine vapor produced perpuff, over the discharge cycle of the battery (unless some additionalcompensatory methods are employed to counter this decline). In contrast,the output voltage of an LFP battery is much more constant at around3.2V, thereby providing a user with a more consistent and reliableexperience, while avoiding the need for any additional compensation ofthe declining voltage. (Note that the voltage levels shown in FIGS. 5and 6 are for an open circuit condition; the voltage under load will besomewhat lower—e.g. approximately by about 0.5V, so 2.7V for the LFPbattery compared with 3.2V for an open circuit.)

FIG. 5 also shows two cut-off lines, marked as C1 and C2. The processor555 (or some other facility within the control unit 20), monitors thevoltage output from the battery 210. When the voltage output falls belowthe specified cut-off level, C1 or C2 (for a commonly-used lithium ionbattery or an LFP battery respectively), the processor 555 preventsfurther operation of the e-cigarette 10, and more specifically of heater365. This cut-off, which can be regarded as the end of the dischargecycle, therefore protects the battery 210 from excessive discharge(which may cause damage to a re-chargeable battery), as well as ensuringthat the user does not receive a compromised experience from thee-cigarette 10 due to the device operating at an unsuitably low voltage.Note that as discussed above, the controller 555 may provide some userindication of the battery status (exhausted, or near exhausted) viaspeaker 558 (and/or via any other available indicator).

FIG. 6 illustrates in schematic form how the power output of the battery210 may vary over a timescale of a single puff, i.e. just a few seconds(this can be regarded as a form of puff profile). The graph compares theoperation (in terms of current output) of a commonly-used lithium ionbattery (dashed line) against the corresponding performance of an LFPbattery (solid line) for an e-cigarette 10.

We assume in FIG. 6 that an inhalation is initiated and detected by asuitable sensor at time=T0. At this point, the controller 555 enablesthe maximum available power from the battery 210 to be supplied to theheater 365. The maximum available power from an LFP battery is shown asP1 in FIG. 6 , while the maximum available power from a commonly-usedlithium ion battery is lower, shown as P2 (where P1>P2). For example,the maximum power output P1 for the LFP battery may reflect a current ofat least 2.5 A, or at least 5 A, potentially up to a maximum of severalamps (e.g. 6, 8 or 10 amps).

At time T1 the heater reaches its preferred operating temperature (forthe e-cigarette having an LFP battery), and the power now falls to alower level P3, which is set so as to maintain the heater at thepreferred operating temperature. Similarly, for an e-cigarette having acommonly-used lithium ion battery, the heater reaches its preferredoperating temperature at time T2, and the power again falls to level P3so as to maintain the heater at the preferred operating temperature.

Since the maximum power output P1 of the LFP battery is greater than themaximum power output P2 of a commonly-used lithium ion battery, the timeT1 taken for an e-cigarette using the former to reach the preferredoperating temperature is less than the time T2 taken for an e-cigaretteusing the latter to reach the preferred operating temperature.Accordingly, an e-cigarette having an LFP battery can provide betterresponsiveness to a user inhalation than an e-cigarette having acommonly-used lithium ion battery.

Note that different types of electrical product present different typesof load to a battery regarding timing and amount of current draw. Forexample, a bicycle lamp will tend to have a prolonged draw (manyminutes) at low to moderate current, whereas an e-cigarette generallyutilizes short pulses of high current for inhalation, with a low levelof current draw between the pulses. These differing load characteristicsmay have an effect on overall battery behavior.

FIG. 7 is a graph showing experimental results from tests on an LFPbattery to simulate behavior in an e-cigarette. The LFP battery undertest had dimensions (form factor) corresponding to a standard AAbattery. A succession of current pulses was drawn from the battery, eachpulse having a current of approximately 4 A and a duration of 3 secondsto simulate an inhalation and the power supplied to operate the heater365. This represents a total of approximately 3.3 mA hours for eachinhalation. The interval between the inhalations was 10 seconds (shorterthan in real usage, but allowing the experiment to be completed morequickly—and still allowing time for the heater to cool betweeninhalations). The current taken during these intervals was 0.005 A, forexample to power controller 555. The total number of 4A current pulsesuntil the battery fully discharged was 106, for a total operating time(including both pulses and pulse intervals) of approximately 1378seconds (just under 23 minutes). The overall measured capacity of thebattery was 0.365 A hours.

The graph of FIG. 7 plots the output voltage and output current from theLFP battery as measured against total capacity (energy, in Amp-hours)drawn so far from the battery. The x-axis (capacity) therefore alsoprovides an indication of time, except that the intervals between pulsesare heavily compressed along the x-axis (compared with their actualduration) because very little energy (capacity) was drawn during theseintervals. The top plotted line in the graph of FIG. 7 represents outputvoltage (as per the scale to the left of the graph in volts), while thelower plotted line in FIG. 7 represents output current (as per the scaleto the right of the graph in amps). The lower line clearly shows theindividual current pulses, each of 4 amps. The top line clearly showsthe drop in voltage which results from putting a load across thebattery. In particular, for each current pulse, the battery voltagedrops from the open circuit value (or very near open circuit value,given the 0.005 A current during the intervals between pulses) down byapproximately 0.3-0.5 volts to the loaded value, when the 4 A current isbeing drawn.

Three horizontal lines, denoted H1, H2 and H3, have been superimposed onthe plot of FIG. 7 . The line H1 indicates the initial level of theminimum battery voltage under load; in fact, this minimum batteryvoltage remains approximately constant for the first half of the batterydischarge lifetime (at least). The lines H2 and H3 are 0.16V and 0.32Vrespectively below line H1—representing a decrease compared with line H1of approximately 5.6% and 11.2% respectively (or slightly under 5% and10% respectively of the open circuit voltage). In addition, the verticalline V¹ indicates where the minimum voltage output from the battery(under load) is found to fall below the line H2. This only occurs oncean energy of about 0.317 A hours has already been drawn from thebattery, which represents about 87% of the overall capacity. In otherwords, FIG. 7 shows that the battery voltage under load for the LFPbattery is constant within a range of ±3% for 85% of the dischargelifetime.

Table 1, shown in FIG. 10 , is derived from the same underlying data setas FIG. 7 , but is represented in tabular form. In particular, the mainportion of Table 1 (i.e. all but the two columns to the far right,enclosed in the high-lighted box), represent the average voltagemeasurement under load for each successive current pulse. Thus the firstrow of FIG. 7 represents the voltage output under load for currentpulses 1-10, the second row of FIG. 7 represents the voltage outputunder load for current pulses 11-20, and so on. The voltage was sampledat a rate of 1 Hz, so three voltage measurements were obtained for eachcurrent pulse (of 3 seconds), and then averaged together to provide thefigures in Table 1. (Note also that a couple of boxes in Table 1 areleft blank where the data did not record properly.) It will beappreciated that the voltage under load figures of Table 1 provide agood representation of the user experience of an e-cigaretteincorporating such an LFP battery, in that the voltage under loadfigures reflect actual operation (inhalation) by the user (whereas theopen circuit voltage figures represent intervals between useroperation).

For the first half of the data (samples 1-53), the voltage outputremains in the range 2.90-2.87V. This is a range of only just over 1%,and hence provides in effect a very constant output level. (Thevariations with this first half of the data may just reflect noise inthe system, minor measurement variations, etc.) After 85% of the chargelifetime (samples 1-90), the average voltage under load has decreased by0.15V from 2.90V to 2.75V. It will be appreciated that this is again amuch smaller decline than would generally be seen for a more commonlyused lithium battery.

Table 1 also shows that there is a further voltage drop of 0.13V as theremaining capacity is taken from the battery. Again, this is a muchsmaller decline than would generally be seen for a more commonly usedlithium battery. In addition, a user is typically less likely toexperience this voltage drop after 85% of the battery capacity has beenused, because in many cases the e-cigarette will already provide someindication (e.g. a warning light) that the battery charge is at arelatively low level (15% or less), and therefore the user willre-charge the e-cigarette at this point (if not before). Moreover, auser is likely to accept that the low remaining battery charge mayresult in a slight decrease in performance, and indeed may take this asconfirmation that the battery should now be re-charged.

In some cases, the battery voltage may be a little higher just at thestart of operation, for the first couple of current pulses (inhalations)or so after the start of discharging from a fully charged state. Thereis a hint of this in FIG. 7 , i.e. a very slight upturn at zero usedcapacity at the far left of the plot. Accordingly, it may be appropriatein some circumstances to discard the first one or two inhalations whenassessing the initial voltage level. On the other hand, for the LFPbattery that was tested, Table 1 shows that this effect is not reallyevident, or only marginally so, for the measured voltage under load ofeven the first current pulse.

The right-hand portion of Table 1 (shown in the highlighted outline)contains two columns. The first (left) one of these columns justprovides the average voltage measurement for that row of the Table. Thiscolumn gives a clear indication of the output voltage beingapproximately constant for the first half of the charge lifetime, andthen a decrease setting in over the second half of the charge lifetime.

The second (right) one of the columns in Table 1 (the rightmost columnin the overall table) represents the average decline in voltage withineach pulse for the pulse samples in that row. Thus as mentioned above,three voltage measurements were obtained for each pulse, and in allcases there is a (small) decline in voltage output from the firstmeasurement through to the third measurement. This decline wascalculated for each pulse on an individual basis, and then averagedacross the pulse samples for each row. This rightmost column shows thattowards the end of the charge lifetime, not only does the averagebattery output fall, but also the rate of decline within an individualpulse also increases. However, this additional decline is of relativelylesser importance if the desired power profile over an individualinhalation broadly follows the shape shown in FIG. 6 —i.e. a higherinitial power output is important to first heat the heater, after whicha reduced power output is generally acceptable.

FIG. 8 is a plot generally similar to that of FIG. 7 , and using thesame battery, however, this time the current pulses are at 5A ratherthan 4 A. This is a relatively high level of current output, such asmight be desired for the initial heating phase shown in FIG. 6 (and alsohelps to compensate for the lower voltage of an LFP battery compared tomore commonly used batteries). As would be expected, the higher currentlevel reduces the overall number of pulses that can be achieved over thecharge lifetime (i.e. until the battery has been discharged), from 106in FIG. 7 , down to 86 for FIG. 8 . Apart from this however, it can beseen that the LFP battery again produces a consistent and predictablevoltage output which is effectively constant for a first half of thedischarge cycle, and even then only undergoes a relatively mild declinein voltage during the second half of the discharge cycle. This isconfirmed by a review of lines V1, H1, H2 and H3, which are provided onthe same basis as for FIG. 7 . Note that line V1, indicating a drop involtage output under load of 0.16V, occurs once 0.321 A hours ofcapacity have been consumed from the battery, similar to the situationin FIG. 7 (where line V1 was positioned at a capacity of 0.317 A hours).

FIG. 9 is a plot generally similar to that of FIG. 8 , again using 5 Acurrent pulses and showing a plot of voltage (top line) and current(lower line) against used capacity (in A hours). The battery tested inFIG. 9 is a lithium manganese cathode cell, rather than an LFP cell. Theform factor of the lithium manganese battery is AA (the same as that ofthe LFP battery for FIGS. 7 and 8 ).

As shown in FIG. 9 , the lithium manganese battery does have anadvantage of higher capacity than the LFP cell of FIGS. 7 and 8 . Inparticular, the lithium manganese battery is found to have a capacity of0.595 A hours, which supported 184 current pulses at 5A. However, theprofile of voltage variation with capacity for the lithium manganesebattery is significantly poorer than the corresponding profile for anLFP battery as shown in FIGS. 7 and 8 . This can be seen by looking atlines V1, H1, H2 and H3 which have again been superimposed on the plot,with H1 representing the voltage level under load at zero used capacity.

The spacing of lines H1, H2 and H3 has been increased to 0.21V (comparedwith 0.16V in FIGS. 7 and 8 —to reflect the greater initial voltage forthe lithium manganese battery compared with the LFP battery, e.g. about4.2V open circuit compared with 3.4V open circuit). However, even withthis greater spacing, we see from the positioning of line V1 that thevoltage under load crosses line H2 (hence a 0.21V drop from zero usedcapacity) at a used capacity of just 0.085 A hours. This represents just14% of the overall capacity of the lithium manganese battery. Indeed, inFIG. 8 the LFP battery crossed the line H2 at a capacity of 0.32 Ahours, so even though the LFP battery has a lower total capacity thanthe lithium manganese battery, it can supply a much greater capacity(both in relative and also absolute terms) at an approximately constantvoltage. Furthermore, the LFP battery exhibits a very consistent voltageoutput level until a capacity of about 0.2 A hours has been used, andonly then starts to decline towards line H2. In contrast, in FIG. 9 , itis clear that the output voltage under load of the lithium manganesebattery starts to drop even after the very first few current pulses.

In addition, not only does the output voltage of the lithium manganesebattery start to decline at a very low used capacity, but this declinecontinues through the lifetime of the battery charge, so that theoverall voltage drop of the lithium manganese battery during a dischargecycle is much greater than for an LFP battery. For example, in FIG. 8 ,the voltage output under load only reaches line H3 (0.32V below theinitial voltage level) once the battery is fully discharged (usedcapacity about 0.36 A hours). In contrast, for FIG. 9 , the voltageoutput under load reaches line H3 (0.42 V below initial voltage level)at a lower used capacity of about 0.24 A hours, and continues to drop byat least the same amount again before the lithium manganese battery isfully discharged.

The plots of FIGS. 7, 8 and 9 confirm that an e-cigarette having an LFPbattery as disclosed herein is able to provide more consistent andpredictable performance, especially in terms of the voltage supply forheater operation at each inhalation, but without involving more costlyor complex electronics. Such a battery may be utilized in a wide rangeof electronic vapor provision systems, for example, for vaporizingnicotine-containing liquids or for producing volatiles fromtobacco-derived plant material (or derivatives thereof).

In order to address various issues and advance the art, this disclosureshows by way of illustration various embodiments in which the claimedinvention(s) may be practiced. The advantages and features of thedisclosure are of a representative sample of embodiments only, and arenot exhaustive and/or exclusive. They are presented only to assist inunderstanding and to teach the claimed invention(s). It is to beunderstood that advantages, embodiments, examples, functions, features,structures, and/or other aspects of the disclosure are not to beconsidered limitations on the disclosure as defined by the claims orlimitations on equivalents to the claims, and that other embodiments maybe utilized and modifications may be made without departing from thescope of the claims. Various embodiments may suitably comprise, consistof, or consist essentially of, various combinations of the disclosedelements, components, features, parts, steps, means, etc., other thanthose specifically described herein. The disclosure may include otherinventions not presently claimed, but which may be claimed in future.

1. A control unit for an electronic vapor provision system, the controlunit comprising: a battery for providing electrical power to a heaterand wherein an output voltage of the battery when 80% discharged bysuccessive puffs of the electronic vapor provision system is no morethan 0.25V below the output voltage of the battery when fully charged.2. The control unit of claim 1, wherein the battery is a lithium ironphosphate battery having a lithium ferrophosphate cathode.
 3. Thecontrol unit of claim 1, wherein the battery has a rated capacity in arange of 250-600 mA hours to support at least 100 puffs of theelectronic vapor provision system, each puff drawing a current of atleast 2.5 A from the battery.
 4. The control unit of claim 1, whereinthe control unit further includes a sensor to detect a user inhalation,and a controller configured to initiate provision of electrical powerfrom the battery to the heater in response to the sensor detecting theuser inhalation.
 5. The control unit of claim 4, wherein in response tothe sensor detecting the user inhalation, the controller is configuredto provide a first phase of electrical power and then a second phase ofelectrical power from the battery to the heater, wherein the first phaseof electrical power has a higher level of electrical current than thesecond phase of electrical power.
 6. The control unit of claim 5,wherein the first phase of electrical power has a current level of equalto or greater than 3 amps.
 7. The control unit of claim 6, wherein thefirst phase of electrical power has a current level of equal to orgreater than 5 amps.
 8. The control unit of claim 1, wherein the outputvoltage of the battery when half discharged is no more than 0.1V belowthe output voltage of the battery when fully charged.
 9. The controlunit of claim 8, wherein the output voltage of the battery when halfdischarged is no more than 0.05V below the output voltage of the batterywhen fully charged.
 10. The control unit of claim 1, wherein the outputvoltage of the battery when half discharged is no more than 3% below theoutput voltage of the battery when fully charged.
 11. The control unitof claim 8, wherein the output voltage of the battery when halfdischarged is no more than 1.5% below the output voltage of the batterywhen fully charged.
 12. The control unit of claim 1, wherein the outputvoltage of the battery when 80% discharged is no more than 0.16V belowthe output voltage of the battery when fully charged.
 13. The controlunit of claim 1, wherein the output voltage of the battery when 80%discharged is no more than 6% below the output voltage of the batterywhen fully charged.
 14. The control unit of claim 1, wherein the outputvoltage of the battery is measured under load when providing electricalpower to the heater to produce vapor.
 15. The control unit of claim 14,wherein the output voltage of the battery is in a range of 2.6V-3Vmeasured under load.
 16. The control unit of claim 15, wherein theoutput voltage of the battery is approximately 2.8V measured under load.17. The control unit of claim 1, wherein the output voltage of thebattery is in a range of 3V-3.4V for an open circuit.
 18. The controlunit of claim 17, wherein the output voltage is approximately 3.2V foran open circuit.
 19. The control unit of claim 1, wherein electricalpower is supplied from the battery to the heater without compensationfor variation in output voltage of the battery over a discharge cycle.20. An electronic vapor provision system comprising the control unit ofclaim 1 and the heater.
 21. The electronic vapor provision system ofclaim 20, wherein the heater is located in a cartomizer that isconnected to the control unit.
 22. The electronic vapor provision systemof claim 20, wherein the heater and the control unit are integrated intoa single device.